Electrical system



Aug. 11, 1936. ND 2,050,505

ELECTRICAL SYS TEM Filed May 5, 1950 $Sheets-Sheet 1 4 Modu/zfea 2 Radio Radio Frequency Receiver- Oscil/afi?!" Couk/ea' Rad/O Fig.2. Frequency I2 2 0 ll 7 or Madu/aTea' DI'sTarT/ng Radio Radio Radio Frequency Frequency Receiver Amplifier Amplifier- Audio 1 Frequency d Oscil/afor m MP9 I8 M /6 2s Audio Radia Frequency Receiver Oscil/afor In venTor' Aug. 11, 1936. P, SISKlND ELECTRICAL SYSTEM Filed May 5, 1950 3 Sheets-Sheet 2 Radio Receiver Aug. 11,1936. RR I ND 1 '2,050,505

ELECTRICAL SYSTEM Filed May 5, 1950 5 Sheets-Sheet s w V Bia-M M I 5 a Fig.5.

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MEAL-M Patented Aug. 11, 1936 nsirso STATES ATENT oFFicli 20 Claims.

The present invention relates to electrical systems, and more particularly to systems for calibrating the frequency of electrical circuits, such as those of receiving sets.

According to present-day practice, receiving sets are calibrated by means of oscillators, set

successively to oscillate at particular frequencies, say 1400, 1500, etc. kilocycles, by means of a standard wave meter. The receiving set is coupled to the oscillator, and its dial is calibrated, in terms of frequency, to correspond to each of the frequencies thus obtained. The process is very wasteful of time and expensive, and requires very accurate settings, both of the oscillator and the receiving set, corresponding to each frequency observed.

It is an object of the present invention tosimplify and improve upon present-day practice, with a View to economizing upon time and expense. Other objects will be explained hereinafter, and will be particularly pointed out in the appended claims.

With the above ends in View, a feature of the invention resides in subjecting the receiving set to the wave frequency of a modulated oscillator, and causing the set to resonate with successive overtones of that frequency. The fundamental frequency may be very low, say 50 kilocycles, and the effect of the strong fundamental and second overtones may be greatly reduced by a suitable high-pass filter. If desired, the modulations may be brought'about by connecting the oscillator to an amplifier and modulating the amplifier by means of an audio oscillator. A distortion-producing amplifier may be connected between the amplifier and the receiving set for the purpose of enhancing the amplitudes of the overtones.

The invention will now be explained in connection with the accompanying drawings, in which Fig. 1 is a diagrammatic view illustrating a principle of the invention; Fig. 2 is a similar view with additional apparatus; Fig. 3 is a similar view, showing some of the circuit connections; Fig. 4 is a view similar to Fig. 3 of a modification, but showing additional circuit connections; and Fig. 5 is a diagrammatic view of circuits and apparatus constructed according to a preferred embodiment of the present invention.

Referring, first, to Fig. 1, a non-oscillating radio receiver 2 to be calibrated is coupled to a modulated radio-frequency oscillator 4' that may be set, once for all, to any desired frequency, preferably a very low frequency, say 50 kilocycles. The radio receiver 2 is successively adjusted so as to resonate with the successive overtones of the fundamental frequency of the oscillator. The dial of the radio receiver 2 is calibrated to suecessive resonating points corresponding to the said successive overtones, merely by successive tuning of the radio receiver to the successive 5 overtones.

This is the principle underlying the invention. The use of a wave meter is done away with, as the fundamental 50-kilocycle setting may be made in any convenient Way without the use of wave meters, and the necessity for accurate and repeated settings of the oscillator is eliminated. The successive overtones can be picked off readily on the radio receiver 2 as soon as onehas been initially determined, as explained hereinafter, and the calibration over the complete dial range may be efiected in a Very few minutes with exceeding accuracy.

The fundamental frequency of the oscillator 4 may be taken as that frequency difference be tween successive points on the desired calibration curve,for example, the 50,000 cycles per second before mentioned,-as to give twenty calibrated points on the tuning range of the ordinary broadcast receiver (550,000 to 1,500,000 cycles per sec- 0nd). This makes use of the 11th to th overtones or harmonics of the oscillator, but the range may obviously be extended as far as desired, say the 300th overtone.

The oscillator 4 may be self modulated, or it 30 may be modulated from an outside source, as by means of an audio-frequency oscillator 8, as shown in Fig. 2. The combination of the radio and audio oscillators, furthermore, ensures'stability. A radio-frequency oscillator 6 is coupled to a radio-frequency amplifier l0 which is modulated by the audio-frequency oscillator 8. The amplifier I0 excites a distorting radio-frequency amplifier l2, the latter being coupled to the radio receiver 2. The purpose of the distorting radiofrequency amplifier I2 is to enhance the amplitudes or the modulated harmonic frequencies of the amplifier l0, so that they may be the more readily detected in the radio receiver ,2. The strength of the useful overtones of the oscillator might not otherwise be sufiicient .to effect the calibration. V

The radio-frequency oscillator is shown in Fig.

3 as comprising a vacuum tube l4 having a filament IS, a grid l8 and a plate 20. The oscillator has grid and plate coils Hand .24, respectively, coupled together in the usual fashion of tickler coils, the coil 24 being in parallel with a tuning condenser 20, both being in series with a 3 battery 28 shunted by a capacity 30.

The input circuit is provided with a further coil 34 of a transformer 34, 36, the coil 36 of which is in circuit with the audio-frequency oscillator 8. The condenser 32 shunts the coil 34 by-passing the radio-frequency currents. The radio-receiver 2 is coupled to this oscillator and operated in the manner before described.

It has before been stated that the use of a wave meter is unnecessary in the practicing of the present invention. All that is necessary is to determine beforehand one fundamental frequency, as the 50-kilocycle frequency. The oscillator should, of course, be stable, and a convenient way to obtain this fundamental frequency, and also to keep it constant and accurate, is to use a piezo-electric crystal, or a magnetostrictive rod or a tuning fork, or the like. A piezo oscillator 6 is illustrated in Figs. 4 and 5. As Fig. 5 illustrates additional apparatus, it is well to refer to Fig. 4, illustrating a vacuum tube 38 having the filament 40, the grid 42 and the plate 44. A piezo-electric crystal 45 is disposed in the input circuit, shunted by a radio-frequency choke coil 46 and a biasing battery 48, according to well known practice. A block condenser (not shown) may be inserted in series with the crystal, but is omitted from the drawings for clearness. The output circuit of the oscillator contains a coil 50 and a tuning condenser 52 disposed, in parallel, both in seseries with a B battery 54, which is shunted by a bypass condenser 55.

Coils 56 and 58 are connected between the filament 40 and the plate 44, in series with a battery 60 and a blocking condenser 62. The radiofrequency amplifier I0, comprising a vacuumtubei64 having a filament 66, a grid 68 and a plate I0, is coupled to the oscillator 38 by connecting the coils 56 and 58 in its input circuit. The output circuit of the amplifier 64 is supplied with energy by the same B battery 54, in series with a coil 12 in parallel with a tuning condenser 14. The audio-frequency amplifier 8 is coupled to the coil 58 by means of the coil 36, and the radio receiver 2 is operated in the same manner as before described.

The capacity coupling of the amplifier and oscillator shown in Fig. 4 may, of course, be replaced by inductive or other coupling and the same is true of the system of Fig. 5, the connections of which will now be readily understood, the same reference numerals being employed as in Fig. 4. The audio-frequency oscillator 8 is shown in Fig. 5 of conventional type, comprising a vacuum tube I6 having plate and grid coils I8 and coupled together in the usual manner and frequency adjusted by condenser 19, with an output coil 82, coupled to the coil 80, connected with the coupling coil 36. To prevent parasitic o scillations, neutralizing coils and condensers 84 and 86 are further illustrated in Fig. 5, these being omitted from the other figures for clearness. The distorting radio-frequency amplifier I2 is shown comprising a vacuum tube 88 capacity coupled to the amplifier I0 in very much the same way as the latter is coupled to the receiver 2. The distorting amplifier is shown provided with an abnormal negative grid bias 89. A filter 90 is shown connected between the distorting radio-frequency amplifier I2 and the radio-receiver 2. The filter is designed so as to filter out the fundamental and any additional desired overtones. The amplitude of the fundamental, second and third harmonics applied to the radio receiver may otherwise be excessive. A properly designed filter 90 permits reduction in amplitude to a marked degree of the overtones of lower frequency than those required for calibration of the receiver.

The receiver 2 is illustrated in Fig. 5 as comprising, in simple, diagrammatic form, a vacuum tube 92, the output circuit of which is provided with a telephone or loud speaker 94 and the input circuit of which is provided with a tuning condenser 96 and a coil 98, the latter coupled to a coil I00, grounded at I02 and connected with the filter 90 by a conductor I04. A variable condenser I06 connected in the conductor II6 may serve the double purpose of adjustment of input to receiver and also as part of the filter arrangement 90.

One of the harmonics must be identified by some suitable means. This may conveniently be accomplished by the use of an auxiliary radiofrequency oscillator I08 whose fundamental frequency is adjusted, by means of a wavemeter, or otherwise, to that of one of the harmonic frequencies of the main oscillator frequency used in calibrating the radio receiver, say 1500 kilocycles. This frequency is adjusted by the variable condenser I09 and tuning coils H0 and III.

A slight adjustment, one kilocycle more or less, of this auxiliary oscillator frequency, then, will give, in addition to the modulation frequency of the oscillator 8, an audible beat note in the radio receiver when it is tuned to this particular frequency as, for example, 1500 kilocycles. This beat note can be made somewhat different in frequency from that of the audio oscillator frequency used and thereby distinguish that one harmonic frequency from all the others by a difierence in tone.

The auxiliary oscillator is shown provided with an output coil I I2 that is connected in series with a variable condenser H4 in a conductor II6 that is connected with the conductor I04.

All the apparatus, except the coupling coil I00, is shielded by a suitable shield II8 to prevent any direct pickup except through the coupling coil I00. This protects the radio receiver 2 from all oscillations except the frequencies passed by the filter and those of the auxiliary oscillator I08.

Modifications will obviously occur to persons skilled in the art, and all such are considered to fall within the spirit and scope of the present invention, as defined in the appended claims.

What is claimed is:

l. A method of calibrating a tunable circuit that comprises simultaneously impressing upon the circuit a plurality of modulated electric waves of constant, predetermined frequencies within the tuning range of the circuit, successively tuning the circuit to effect demodulation of each of the impressed modulated waves, successively, and indicating the position of tuning at which each successive modulated wave is demodulated to calibrate the circuit.

2. A method of calibrating a tunable circuit that comprises simultaneously impressing upon the circuit a plurality of modulated electric waves of constant, predetermined frequencies within the tuning range of the circuit, successively tuning the circuit to effect demodulation of each of I the impressed modulated waves, successively, indicating the position of tuning at which each successive modulated wave is demodulated to calibrate the circuit, and beating with one of the modulated waves to distinguish the position corresponding to said modulated wave from the other positions.

3. A method of calibrating a tunable, radioreceiving instrument that is provided with an output device, the said method comprising simultaneously impressing upon the instrument a group of overtones of a modulated-wave frequency within the tuning range of the instrument, successively tuning the instrument to effect demodulation of the successive overtones, thereby producing audible tones in the output device, and calibrating the instrument to correspond to the successively produced audible tones.

4. A method of calibrating a tunable, radioreceiving instrument that is provided with an output device, the said method comprising simultaneouslyimpressing upon the instrument a group of overtones of a modulated wave frequency within the tuning range of the instrument, successively tuning the instrument to effect demodulation of the successive overtones, thereby producing audible tones in the output device, calibrating the instrument to correspond to the successively produced audible tones, and

beating with one of the overtones to produce a further audible tone in the output device, thereby distinguishing said one overtone from the other overtones.

5. An electrical system having, in combination, an oscillator, an amplifier connected therewith, anoscillator for modulating the frequency of the amplifier, and a distortion-producing amplifier for enhancing the amplitude of the overtones of the modulated frequency.

6. An electrical system having, in combination, an oscillator, an amplifier connected therewith, an oscillator for modulating the frequency of the amplifier, a distortion-producing amplifier for enhancing the amplitude of the overtones of the modulated frequency, the distortion-producing amplifier having an output coil, and means for shielding the system, the output coil being disposed without the shielding means.

7. An electrical system having, in combination, a modulated oscillator, means for connecting the oscillator to a receiving set, and means for filtering out predetermined overtones from the modulated oscillator.

8. A calibrating system for radio-receiving instruments having, in combination, a modulated oscillator, means for connecting the oscillator with the receiving instrument to impress upon the instrument a group of overtones of a modulated wave frequency of the modulated oscillator within the tuning range of the instrument, means for successively tuning the instrument to effect demodulation of the successive overtones, whereby the positions of tuning at which the successive overtones are demodulated may be indicated to calibrate the instrument, an auxiliary oscillator, and means for connecting the auxiliary oscillator with the instrument to cause beats to be produced between one of said overtones and the auxiliary oscillator to distinguish said one of the overtones from the other overtones.

9. An electrical system having, in combination, an oscillator, an amplifier connected therewith, an oscillator for modulating the frequency of the amplifier, a distortion-producing amplifier for enhancing the amplitude of the overtones of the modulated frequency, means for shielding the system, and means for filtering out predetermined overtones from the distortion-producing amplifier output.

10. A calibrating system for radio-receiving instruments having, in combination, a modulated oscillator, a distortion-producing amplifier for enhancing the amplitudes of the overtones of the modulated frequency, means for connecting the amplifier with the receiving instrument to impress upon the instrument a, group of overtones of a modulated wave frequency of the modulated oscillator within the tuning range of the instrument, means for successively tuning the instrument to effect demodulation of the successive overtones, whereby the positions of tuning at which the successive overtones are demodulated' may be indicated to calibrate the instrument, and means for electrically identifying one ofthe overtones.

11. An electrical system having, in combination, a modulated oscillator, a distortion-producing amplifier for enhancing the amplitudes of the overtones of the modulated frequency, and a high-pass filter for reducing the amplitudes of certain undesired frequencies in the distortionproducing amplifier output.

12. An electrical system having, incombination, an oscillator, an amplifier connected therewith, an oscillator for modulating the frequency of the amplifier, a distortion-producing amplifier for enhancing the amplitudes of the overtones of the modulated frequency, a high-pass wave-filter for reducing the amplitudes of certain undesired 9 frequencies in the output of the distortion-producing amplifier, an output coil connected to the wave-filter through a variable condenser, and means for shielding the system, the output coil being disposed without the shielding means.

13. An electrical system having, in combination, an oscillator, an amplifier connected therewith, an oscillator for modulating the frequency of the amplifier, a distortion-producing amplifier for enhancing the amplitudes of the overtones of the modulated frequency, a high-pass wave-filter for reducing the amplitudes of certain undesired frequencies in the output of the distortion-producing amplifier, an output coil connected to the wave-filter through a variable condenser, an auxiliary oscillator for producing a beat note with one of the'overtones of the modulated frequency thereby identifying that particular overtone and having its output connected through a variable condenser to the output coil of the wave-filter, and means for shielding the system, the output coil being disposed without the shielding means.

14. A calibrating system for a tunable circuit having, in combination, means for simultaneously impressing upon the circuit a plurality of overtones of a modulated-wave frequency within the tuning range of the circuit, means for successively tuning the circuit to effect demodulation of each of the successive overtones, whereby the positions of tuning at which the successive overtones are demodulated may be indicated to calibrate the circuit, and means for identifying one of the overtones.

15. A calibrating system for a tunable circuit having, in combination, means for simultaneously impressing upon the circuit a plurality of overtones of a modulated-wave frequency within the tuning range of the circuit, means for successively tuning the circuit to effect demodulation of each of the successive overtones, whereby the positions of tuning at which the successive overtones are demodulated'may be indicated to calibrate the circuit, and means for beating with one of the overtones to distinguish said one overtone from the other overtones.

16. A calibrating system for a tunable, radioreceiving instrument provided with an output device having, in combination, means for simultaneously impressing upon the instrument a group of overtones of a modulated-wave frequency within the tuning range of the instrument, means for successively tuning the instrument to effect demodulation of the successive overtones, thereby producing audible tones in the output device, whereby the positions of tuning at which the successive overtones are demodulated may be indicated to calibrate the instrument to correspond to the successively produced audible tones, and means for identifying one of the overtones.

17. A calibrating system for a tunable, radioreceiving instrument provided with an output device having, in combination, means for simultaneously impressing upon the instrument a group of overtones of a modulated Wave frequency within the tuning range of the instrument, means for successively tuning the instrumentto effect demodulation of the successive overtones, thereby producing audible tones in the output device, whereby the positions of tuning at which the successive overtones are demodulated may be indicated to calibrate the instrument to correspond to the successively produced audible tones, and means for beating with one of the overtones to produce a further audible tone in the output device, thereby distinguishing said one overtone from the other overtones.

18. A calibrating system for radio-receiving instruments having, in combination, a modulated oscillator adapted to produce overtones of a modulated-wave frequency, means for connecting the oscillator with the receiving instrument to impress upon the instrument a group of the said overtones within the tuning range of the instrument, means for successively tuning the instrument to effect demodulation of the successive overtones, whereby the positions of tuning at which the successive overtones are demodulated may be indicated to calibrate the instrument, and means for identifying one of the overtones.

19. A method of calibrating a tunable circuit that comprises simultaneously impressing upon the circuit a plurality of distorted overtones of a modulated-wave frequency within the tuning range of the circuit, successively tuning the circuit to effect demodulation of each of the successive overtones, and calibrating the circuit to correspond to the successive overtones;

20. A calibrating system for a tunable circuit having, in combination, means for impressing upon the circuit a plurality of overtones of a modulated-wave frequency within the tuning range of the circuit, and means for successively tuning the circuit to effect demodulation of each of the successive overtones, whereby the position of tuning at which the successive overtones are demodulated may be indicated to calibrate the circuit.

ROBERT PEER. SISEND. 

